Proton irradiation

The sources used in Ni Mossbauer work mainly contain Co as the parent nuclide of Ni in a few cases, Cu sources have also been used. Although the half-life of Co is relatively short (99 m), this nuclide is much superior to Cu because it decays via P emission directly to the 67.4 keV Mossbauer level (Fig. 7.2) whereas Cu ti/2 = 3.32 h) decays in a complex way with only about 2.4% populating the 67.4 keV level. There are a number of nuclear reactions leading to Co [4] the most popular ones are Ni(y, p) Co with the bremsstrahlung (about 100 MeV) from an electron accelerator, or Ni(p, a) Co via proton irradiation of Ni in a cyclotron. 

Ta metal under proton irradiation Study of radiation effects of the Ta(p, n) W reaction in Ta foil, recording of emission spectra before and after annealing with metallic Ta absorber, and of absorption spectra before and after annealing W/W source... 

T1 is produced by proton irradiation of an enriched T1 target to yield Pb (/1 /2 = 9.4 h), which then decays by positron emission and electron capture to 201T1 ... 

Another procedure for calculating the W value has been developed by La Verne and Mozumder (1992) and applied to electron and proton irradiation of gaseous water. Considering a small section Ax of an electron track, the energy loss of the primary electron is S(E) Ax, where S(E) is the stopping power at electron energy E. The average number of primary ionizations produced over Ax is No. Ax where o. is the total ionization cross section and N is the number density of molecules. Thus, the W value for primary ionization is 0)p = S(E)/No.(E). If the differential ionization cross section for the production... 

For proton irradiation, asymptotic is reached at 500 KeV. The computed integral W value, 28.9 eV, compares well with experimental determination (30.5 eV Christophorou, 1971) fi)p at this energy is calculated to be 53.5 eV, showing great importance of secondary ionization. 

The interaction of neutrons with organic molecules occurs mainly through knock-on of protons. Thus, the radiation chemistry is similar to proton irradiation. Radiation chemistry by positive ions is of increasing importance on account of ion implantation technology, plasma development and deposition processes, and cosmic irradiation. 

Early proton irradiation within the solar system... 

Clayton DD (1989) Origin of heavy xenon in meteoritic diamonds. Astrophys J 340 613-619 Clayton DD, Dwek E, Woosley SE (1977a) Isotopic anomalies and proton irradiation in the early solar system. Astrophys J 214 300-315... 

Lee DC, Halliday AN, Snyder GA, Taylor LA (1997) Age and origin of the moon. Science 278 1098-1103 Lee T (1978) A local proton irradiation model for the isotopic anomalies in the solar system. Astrophys J 224 217-226... 

Figure 28 Schematic presentation of the relative situation of the different types of radiations used in therapy. Two criteria are considered the physical selectivity and the LET (or radiobiological properties). For the low-LET radiations, the physical selectivity was improved from the historical 200-kV x-rays to cobalt-60 gamma rays and the modern linacs. Even with the linacs today, significant improvement is continuously achieved (IMRT, etc.). Among the low-LET radiation, the proton beams have the best physical characteristics, but one of the issues is the proportion of patients who will benefit from proton irradiation. A similar scale can be drawn for high-LET radiation the heavy-ion beams have a physical selectivity similar to protons. Selection between low- and high-LET radiation is a biological/medical problem it depends on the tumor characteristics, and reliable criteria still need to be established (see text). (From Ref 54.)...

Exposed to single brief whole-body proton irradiation (protons in the energy range encountered by astronauts) ranging between 0.25 and 12 Gy and observed for 24 years until death... 

The extremely low abundance is the result of two factors, the relative fragility of the isotopes of Li, Be, and B and the high binding energy of 4He, which makes the isotopes of Li, Be, and B unstable with respect to decay/reactions that lead to 4He. For example, the nuclei 6Li, 7Li, 9Be, nB, and 10B are destroyed by stellar proton irradiations at temperatures of 2.0, 2.5, 3.5, 5.0, and 5.3 x 106 K, respectively. Thus, these nuclei cannot survive the stellar environment. (Only the rapid cooling following the Big Bang allows the survival of the products of primordial nucleosynthesis.)... 

This prototype drug208, 217, has been 11 C-labelled209 for assessment of serotonin uptake sites in depressed patients by reaction of [nC]iodomethane with desmethylcitalopram, 218, in 18-66% radiochemical yield (equation 114). 217 has been obtained also by Dan-nals and coworkers210 by reacting freshly prepared desmethylcitalopram dissolved in DMF with [nC]methyl iodide. The radiochemical yield based on [nC]CH3l was about 20% the overall radiochemical yield was about 9% based on the initial activity of [UC]CC>2 produced by 16 MeV proton irradiation of nitrogen gas in biomedical cyclotron. 

Figure 7. A and B. Map and topographic cross-sectional view of sample locations from Shuster et al. s (2005) study of incision of the Kliniklini valley, Coast Mountains, British Columbia. C. Model thermal histories for each sample, derived from 4He/3He evolution of step-heating experiments on proton-irradiated samples, and bulk grain (U-Th)/He dates. Samples from the valley bottom require rapid cooling, from 80 °C to surface temperatures, at 1.8 0.2 Ma, and samples from higher elevations require thermal histories with progressively smaller extents of cooling (beginning at 1.8 Ma) with elevation. The highest sample (TEKI-23) was at surface temperature before the 1.8 Ma cooling event experienced by the other samples. Collectively, these data are interpreted to be the result of -2 km incision at 1.8 Ma. After Shuster et al. (2005).

Enstatite The first extensive observations of CL in meteorites were for enstatite (MgSiC>3) probably because it shows particularly brilliant CL colors and it is the major mineral in the enstatite achondrites. The visual CL is commonly described as blue, red or less commonly purple and the early spectra, mainly from powdered samples and using proton irradiation, clearly showed the presence of a blue and red emission (4-6). These emissions were confirmed using electron irradiation and spectra showed a blue peak near 400-420nm... 

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